the mini gelatin gliders disappeared out of the battle colisium and there were still over 73000 left to battle

They should be back up shortly. There was a problem with wins not counting towards the achievement, so they were taken down to work on that. Apparently the problem has been isolated and the battle admins have said they're almost done fixing it.

From the news post:

thank you for the info i will keep an out for them to come back